In 1919, British scientists led extraordinary expeditions to Brazil and Africa to test Albert Einstein’s revolutionary new theory of general relativity in what became the century’s most celebrated scientific experiment. The result ushered in a new era and made Einstein a global celebrity by confirming his dramatic prediction that the path of light rays would be bent by gravity. Today, Einstein’s theory is scientific fact. Yet the effort to “weigh light” by measuring the gravitational deflection of starlight during the May 29, 1919, solar eclipse has become clouded by myth and skepticism. In No Shadow of a Doubt, Daniel Kennefick provides definitive answers by offering the most comprehensive and authoritative account of how expedition scientists overcame war, bad weather, and equipment problems to make the experiment a triumphant success.

What compelled you to write this book?

The story of the 1919 eclipse is one of the most dramatic and significant in the history of science, and one that I’ve always found fascinating. What compelled me to research it closely was my puzzlement about the criticisms of Eddington which I heard repeated more and more, especially while working on volume 9 the Collected Papers of Albert Einstein, which covered Einstein’s life during the year 1919. I found the complaints about Eddington’s supposed bias in favor of Einstein unconvincing, especially the claim that Eddington’s pacifism was responsible for his desire to prove Einstein right. I thought that it was time someone looked closely at the actual data analysis decisions, using original documents preserved in the archives. I decided to write the book because I found the complete story of the eclipse which I put together to be fascinating and the centenary seemed like a perfect occasion to tell that story. I also felt that there was a danger that important work on the 1919 eclipse was being overlooked. As part of my research I learned that a re-analysis of the photographic plates taken in 1919 was conducted in 1978 by English astronomers at the Royal Greenwich Observatory using modern plate-measuring equipment and computers. They completely vindicated the work of the original team, and yet their re-analysis had gone totally unrecognized and unread. It was even misrepresented in the one book which did allude to it, Stephen Hawking’s A Brief History of Time. So I felt it was important to restore some balance to the story of what happened in 1919.

You say that the 1919 solar eclipse is perhaps one of the most important eclipses in history, but there are critics who contend that Arthur Eddington placed too much emphasis on the eclipse proving Einstein’s theory of relativity. Why do you think that’s a weak counter-argument?

The problem here is that the modern critics distort the story by their focus on just one participant, the famous astrophysicist Eddington. Incidentally, he was known to his family by his middle name Stanley; he never went by Arthur. Since Eddington was only involved in this one test of general relativity, it is easy to make it seem that there has been too much emphasis on the 1919 eclipse test. But Eddington himself never regarded confirmation of the theory as depending upon this one test. It’s just that modern commentary rarely talks about anything beyond Eddington’s role, which doesn’t even tell the complete story of this one test. There were two expeditions in 1919, and Eddington was only involved in one of them. The other one, organized by the Royal Observatory, Greenwich to Sobral in Brazil, obtained the most important data.

Having said all that, there is a sense in which the 1919 test was of very special importance. There were only three tests of Einstein’s new theory of gravity that were possible to do a century ago. One of these—the explanation of the perihelion shift of Mercury—was impressive, but since Einstein knew the result his theory had to “predict” it didn’t count as a prediction in the usual sense. The other test was the solar redshift measurements, but this confirms only the principle of equivalence and is not strictly speaking a test of general relativity as such. The prediction that light is deflected when it passes through the gravitational field of the Sun was a test of the complete theory that Einstein could not know the answer to beforehand. The 1919 expeditions were the first time that this observation had ever been successfully made. The agreement achieved was very dramatic and the fact that the experiment could not be repeated until the next suitable eclipse, in 1922, added even more drama to the occasion. So the truth is that the 1919 expedition was a special occasion in the history of science.

Can you talk a bit about the circumstances surrounding the Principe and Brazil expeditions that made this experiment so significant?

There were three circumstances that made this eclipse extraordinary. The first is that the eclipse took place on a day, May 29th, when the Sun is in the star field of the Hyades cluster. This is the closest star cluster to the Earth and there is no other place on the ecliptic (the Sun’s path through the sky) with so many bright stars so close together. Thus, an eclipse taking place on that day is perfectly suited to performing this experiment. Such an eclipse will next occur in 2310, so the expedition planners realized that it was especially important to try the experiment in 1919. Unfortunately, as late as November 1918, it looked unlikely that ships could be found to carry the teams to their preferred stations on the island of Principe and in northeastern Brazil. The reason for the suspension of shipping was World War I which fortunately ended abruptly later that same month. Had the war lasted any longer, it is unlikely that the expeditions could have departed. Even as it was a civil war broke out in Portugal, a key stop on their route, before their departure, and Eddington had no idea which ship would take him to Principe when he left England in March 1919.

This second circumstance, that of a war torn world, very nearly scuppered the planning for the expeditions, but undoubtedly helped make the team so famous when they returned successfully. The triumph of science over the tribulations of history really caught the public imagination. Certainly an aspect of this public response was that the expedition was mounted from England in order to test, and confirm, the theory of a German scientist, Albert Einstein, so it had an additional aura of reconciliation about it, at a time when postwar feelings were very bitter.

A third favorable circumstance was the relevant expertise of the expeditions’ personnel, especially the director of the Greenwich Observatory, Frank Watson Dyson. Einstein’s prediction was that the presence of the Sun near stars would cause tiny shifts in their positions, because the Sun’s gravity would deflect the starlight on its way to the Earth. Dyson and Eddington, but especially Dyson, were experts in this kind of differential astrometry, the measurement of small shifts in star positions. They had spent years (decades, in Dyson’s case) measuring the proper motion and the parallax of stars, which depends on the measurement of similar small star shifts. Thus by good fortune this special opportunity to test Einstein’s opportunity was undertaken by the ideal team who were able to overcome all obstacles, including bad weather and difficulties with instrumentation.

Will we ever see a solar eclipse quite like this in our lifetime?

No, we won’t. Obviously an eclipse with this special star field won’t occur again for nearly two centuries. But in addition, the advance of technology means that there are few important scientific tasks which require an eclipse. Radio telescopes do not require a solar eclipse to test Einstein’s light deflection prediction. These instruments can do the test far more accurately than can be done with optical telescopes at an eclipse. But in another sense, replicating the drama of 1919 is open to anyone. Experiments at the recent 2017 eclipse have shown that a modern amateur astronomer can do the experiment alone to an accuracy better than what was achievable in 1919. Another total solar eclipse will cross America in 2024 and we can hope that other enthusiasts will study the eclipse then. If enough people do the experiment and are able to pool their data, they could achieve a result far more accurate than any ever achieved by professional astronomers at an eclipse. We are living at a moment in history in which the means to do this experiment are within the reach of many people.

What do you hope that readers will take away from this book?

What first made me skeptical of Eddington’s modern critics was their claim that the expedition’s work was influenced by Eddington’s bias in favor of General Relativity as well as his militant pacifism. I found these arguments unpersuasive because I knew that Eddington’s views were highly unusual. Other astronomers of the period were highly skeptical of, or even hostile towards, general relativity. War resisters like Eddington (and Einstein) were a despised minority during World War I. It didn’t make sense that this man could have single-handedly persuaded everyone involved to share his peculiar biases. Sure enough, careful reading of the documents in the archives, including letters and data analysis notes, made it clear that the decisions which were being criticized today weren’t even taken by Eddington but by others in the expedition, especially Dyson. Both Eddington and Dyson made it clear in their letters that Dyson was skeptical of Einstein’s theory to begin with. As I puzzled through Dyson’s notes, I began to unravel the reasoning behind his decision, and I found that it made a lot more sense than did the arguments of some of the modern critics. Furthermore, his reasoning is completely vindicated by the results of the 1978 re-analysis. But I also came to realize that Dyson’s decision depended heavily on input from his assistant, Charles Davidson, and that the success of the expedition was made possible by the multinational Astrographic project, which Dyson worked on and which two of the telescope lenses they used were constructed for. I realized I needed to learn about the man who made those lenses, a fellow Irishman called Howard Grubb, and about the institutional framework which was used to organize the expeditions at a very difficult time. The minutes of the meetings of that Joint Permanent Eclipse Committee and the letters written home to his mother and sister by Eddington made the expeditions come alive for me, and I wanted to share that with other readers. I hope they come away, as I did, with a conviction that the history of science cannot be told fully without understanding the role of all the scientists involved, rather than just one or two famous names. Part of the charm of the story is the different characters who contributed to doing something extraordinarily challenging under impossibly difficult circumstances.

New Scientist Live is an annual festival in London which attracts over 30,000 visitors across four days. Each year a huge hall in the ExCel Centre in London is transformed into a hub for all things science and technology, with talks running all day across six stages from some of the world’s greatest minds in the field.

The festival is a great opportunity for Princeton University Press to really get to know the readers of our science titles and see what they’re really engaged with at the moment. It’s always surprising and humbling to see so many younger readers at New Scientist Live so engaged with what we produce and invested in on-trend scientific topics. This really did remind us that, although New Scientist Live does exhibit the greatest minds of our time, it really is the stomping ground for the minds of tomorrow!

Rees signs his first-ever copy of On the Future

This was Princeton University Press’ second year at the festival and our best yet. We came armed with postcards, tote bags, lots of catalogues and copious amounts of badges which were a hit with the visiting school groups. It was also a great year for book sales on our stand – we topped last year’s sales by 11% with The Little Book of Black Holes and The Little Book of String Theory as some of our bestsellers.

One of the highlights of New Scientist Live as far as Princeton University Press was concerned was a wonderful talk by Martin Rees, the Astronomer Royal and member of the House of Lords, whose book, On the Future: Prospects for Humanity is published imminently. Lord Rees spoke to a rapt crowd, many of whom had to stand at the back or sit on the floor; such was his talk’s popularity. Rees discussed three themes from within his book: biotechnology, AI, and space travel. We found the whole talk really interesting, but were particularly fascinated by Rees’s forecast regarding the future of the human body in space. As Rees put it in his book:

The space environment is inherently hostile for humans. So, because they will be ill-adapted to their new habitat, the pioneer explorers will have a more compelling incentive than those of us on Earth to redesign themselves. They’ll harness the super-powerful genetic and cyborg technologies that will be developed in coming decades. These techniques will be, one hopes, heavily regulated on Earth, on prudential and ethical grounds, but ‘settlers’ on Mars will be far beyond the clutches of the regulators. We should wish them good luck in modifying their progeny to adapt to alien environments. This might be the first step towards divergence into a new species. Genetic modification would be supplemented by cyborg technology—indeed there may be a transition to fully inorganic intelligences. So, it’s these space-faring adventurers, not those of us comfortably adapted to life on Earth, who will spearhead the post human era.

Speaking about Stephen Hawking. Also on the stage was our author, Stuart Clark.

Martin Rees also participated in a panel event on the legacy of the late Professor Stephen Hawking. He was joined by Jennifer Ouellette, Marika Taylor, Tom Shakespeare, and our very own Stuart Clark. They discussed Hawking’s work in furthering our understanding of space, in closing the gap between various different scientific communities, and his work as an advocate for the disabled community. Martin Rees shared memories from his time with Hawking at Cambridge, and Marika Taylor shared Hawking’s love of night clubs and salsa bars. It was a very moving occasion.

After a successful 2018 at New Scientist Live, we are looking forward to exhibiting next year’s festival and all the exciting new ideas it will put on show.

Astronomer David A. Weintraub thinks it won’t be long before we are faced with this question not as a hypothetical, but as a real option. Based on the pace of research and the growing private interest in space exploration, humans might be considering trips to Mars before the next century.

In his new book Life on Mars: What to Know Before We Go, Weintraub argues that would-be colonizers of the red planet should first learn whether life already exists on Mars. Just as colonization of various parts of Earth has historically decimated human, animal, and plant populations, so, argues Weintraub, will human colonization of Mars dramatically affect and likely destroy any life that might already exist on Mars. Before we visit, we need to know what – and whom – we might be visiting.

While scientists have yet to determine whether life exists on the red planet, they agree that if Martians do exist, they probably aren’t little green men. So where does our popular idea of Martians come from? Artists and writers have been imagining and depicting Martian life in a variety of ways since long before space travel was a reality. Check out these descriptions of imagined Martian life from over one hundred years ago.

Cover of The Martian, by George du Maurier

In George du Maurier’s 1897 gothic science fiction story The Martian, Martians are described as furry amphibians who are highly skilled in metalworking and sculpting:

“Man in Mars is, it appears, a very different being from what he is here. He is amphibious, and descends from no monkey, but from a small animal that seems to be something between our seal and our sea-lion….

“His five senses are extraordinarily acute, even the sense of touch in his webbed fingers and toes….

“These exemplary Martians wear no clothes but the exquisite fur with which nature has endowed them, and which constitutes a part of their immense beauty….

“They feed exclusively on edible moss and roots and submarine seaweed, which they know how to grow and prepare and preserve. Except for heavy-winged bat-like birds, and big fish, which they have domesticated and use for their own purposes in an incredible manner (incarnating a portion of themselves and their consciousness at will in their bodies), they have cleared Mars of all useless and harmful and mutually destructive forms of animal life. A sorry fauna, the Martian—even at its best—and a flora beneath contempt, compared to ours.”

“How the Earth Men Learned the Martian Language,” from Edison’s Conquest of Mars by Garrett P. Serviss

In Garrett Serviss’s Edison’s Conquest of Mars (1898), on the other hand, Martians are huge creatures, two to three times as tall as a human:

“It is impossible for me to describe the appearance of this creature in terms that would be readily understood. Was he like a man? Yes and no. He possessed many human characteristics, but they were exaggerated and monstrous in scale and in detail. His head was of enormous size, and his huge projecting eyes gleamed with a strange fire of intelligence. His face was like a caricature, but not one to make the beholder laugh. Drawing himself up, he towered to a height of at least fifteen feet.”

Edwin Lester Arnold, in Lieut. Gullivar Jones: His Vacation, published in 1905, describes Martians instead as “graceful and slow,” with an “odor of friendly, slothful happiness about them”:

“They were the prettiest, daintiest folk ever eyes looked upon, well-formed and like to us as could be in the main, but slender and willowy, so dainty and light, both the men and the women, so pretty of cheek and hair, so mild of aspect, I felt, as I strode amongst them, I could have plucked them like flowers and bound them up in bunches with my belt. And yet somehow I liked them from the first minute; such a happy, careless, light-hearted race, again I say, never was seen before.”

“The old man sat and talked with me for hours,” from A Princess of Mars by Edgar Rice Burroughs

And in Edgar Rice Burroughs’ A Princess of Mars, published in 1917, Martians are finally depicted as the little green men of the popular imagination:

“Five or six had already hatched and the grotesque caricatures which sat blinking in the sunlight were enough to cause me to doubt my sanity. They seemed mostly head, with little scrawny bodies, long necks and six legs, or, as I afterward learned, two legs and two arms, with an intermediary pair of limbs which could be used at will either as arms or legs. Their eyes were set at the extreme sides of their heads a trifle above the center and protruded in such a manner that they could be directed either forward or back and also independently of each other, thus permitting this queer animal to look in any direction, or in two directions at once, without the necessity of turning the head.

“The ears, which were slightly above the eyes and closer together, were small, cup-shaped antennae, protruding not more than an inch on these young specimens. Their noses were but longitudinal slits in the center of their faces, midway between their mouths and ears.

“There was no hair on their bodies, which were of a very light yellowish-green color. In the adults, as I was to learn quite soon, this color deepens to an olive green and is darker in the male than in the female. Further, the heads of the adults are not so out of proportion to their bodies as in the case of the young.”

To learn more about Martians in popular culture, the history of planetary astronomy, and the scientific search for life on Mars, read David Weintraub’s Life on Mars!

On Monday, August 21, people all across the United States will witness one of the rarest and most spectacular of all astronomical phenomena: a total solar eclipse. This occurs when the position of the Moon and the Sun in the sky align perfectly, such that the Moon’s shadow falls onto a specific point on the Earth’s surface. If you are lucky enough to be standing in the shadow, you will see the Sun’s light completely blocked by the Moon: the sky will become dark, and the stars and planets will become visible. But because the apparent sizes of the Moon and the Sun are almost the same, and because everything is in motion—the Moon orbits Earth, and Earth rotates around its axis and orbits the Sun—the Moon’s shadow moves quickly. During the eclipse, the Moon’s shadow will cross the United States at a speed of 1800 miles per hour, taking about 90 minutes to travel from the Pacific Coast in Oregon to touch the Atlantic in South Carolina. This means that totality, the time when the Sun’s disk is completely covered as seen from any given spot along the eclipse path, is very brief: 2 minutes and 40 seconds at best.

If you are standing along the eclipse path, it takes about 2.5 hours for the Moon to pass across the Sun. That is, you will see the disk of the Sun eaten away, becoming an ever-narrowing crescent. During this time, you can only look at the Sun with eclipse glasses (make sure they are from a reputable company!), which block the vast majority of the light from the Sun. It is also fun to look at the dappled shadows underneath a leafy tree; if you look closely, you’ll see that the individual spots of light are all crescent-shaped. A bit more than an hour after the Moon begins to cover the Sun, you reach the point of totality, and the sky becomes dark. It is now safe to remove your eclipse glasses.

Experiencing a few minutes of darkness in the middle of the day is pretty cool. But what makes the eclipse really special is that with the light of the Sun’s disk blocked out, the faint outer atmosphere of the Sun, its corona, becomes visible to the naked eye. The corona consists of tenuous gas extending over millions of miles, with a temperature of a few million degrees. It is shaped by the complex magnetic field of the Sun, and may exhibit a complex arrangement of loops and filaments: indeed, observations of the solar corona during eclipses have been one of the principal ways in which astronomers have learned about its magnetic field. The sight is awe-inspiring; those who have experienced it say that it is as a life-changing experience.

As the Moon starts to move off the disk, the full brightness of the Sun becomes visible again, and you must put your eclipse glasses back on to protect your eyes. The Sun now appears as a narrow and ever-widening crescent. A bit more than an hour later, the Sun’s disk is completely uncovered.

The shadow of the Moon will be about 70 miles in diameter at any given time. That means that if you are not standing in that 70-mile-wide path as the shadow crosses the country, you will only see a partial solar eclipse, in which you will see the Sun appearing as a crescent. Again, be sure to wear eclipse glasses to look at the Sun!

Solar eclipses happen roughly once or twice a year somewhere on Earth’s surface, but because of the narrowness of the eclipse path, the number of people standing in the path is usually relatively small. This one, crossing the entire continental US, is special in this regard: tens of millions of people live within a few hours of the eclipse path. This promises to be the most widely seen and recorded eclipse in history! I have never seen a total eclipse of the Sun before, and am very excited to be traveling with my family to Oregon, where we have our fingers crossed for good weather. So, to all those who have the opportunity to stand in the Moon’s shadow, get yourself a pair of eclipse glasses, and prepare yourself to be awed.

We’re pleased to announce that the accompanying microsite to Welcome to the Universe by Neil DeGrasse Tyson, Michael A. Strauss, and J. Richard Gott has won a People’s Choice Webby in the Best Use of Animation or Motion Graphics category. Congratulations to Eastern Standard, the web designer, on a beautifully designed site.

Winning a Webby is especially gratifying because it honors how much fun we had making the site. We knew we wanted an unconventional approach that would mirror both the complexity and accessibility of the book it was meant to promote. Our wonderful in-house team and creative partners, Eastern Standard took on this challenge, and we are so happy with the results.
—Maria Lindenfeldar, Creative Director, Princeton University Press

Creating this microsite was a wonderful experiment for us at Princeton University Press. We wanted to explore how we, as a publisher, could present one of our major books to the public in a compelling way in the digital environment. Ideally, we had a vision of creating a simple site with intuitive navigation that would give readers an inviting mini-tour through the topics of the book, Welcome to the Universe, by Neil deGrasse Tyson, Michael Strauss, and Richard Gott. The animation was meant to be subtle, but meaningful, and to gently encourage user interaction, so that the focus would always remain immersing the reader in the content of the book – what we feel is the most interesting part! We were very happy with how it turned out and now all the more thrilled and honored that the site was chosen for a Webby!
—Ingrid Gnerlich, Science Publisher, Princeton University Press

We’re thrilled to announce that the microsite for Welcome to the Universe by Neil DeGrasse Tyson, Michael A. Strauss, and J. Richard Gott, designed byEastern Standard, has been nominated for a Webby in the Best Use of Animation or Motion Graphics category. Be sure to check it out and vote for the best of the internet!

As an astrophysicist, I am always struck by the fact that even the wildest science-fiction stories tend to be distinctly human in character. No matter how exotic the locale or how unusual the scientific concepts, most science fiction ends up being about quintessentially human (or human-like) interactions, problems, foibles and challenges. This is what we respond to; it is what we can best understand. In practice, this means that most science fiction takes place in relatively relatable settings, on a planet or spacecraft. The real challenge is to tie the story to human emotions, and human sizes and timescales, while still capturing the enormous scales of the Universe itself.

Just how large the Universe actually is never fails to boggle the mind. We say that the observable Universe extends for tens of billions of light years, but the only way to really comprehend this, as humans, is to break matters down into a series of steps, starting with our visceral understanding of the size of the Earth. A non-stop flight from Dubai to San Francisco covers a distance of about 8,000 miles – roughly equal to the diameter of the Earth. The Sun is much bigger; its diameter is just over 100 times Earth’s. And the distance between the Earth and the Sun is about 100 times larger than that, close to 100 million miles. This distance, the radius of the Earth’s orbit around the Sun, is a fundamental measure in astronomy; the Astronomical Unit, or AU. The spacecraft Voyager 1, for example, launched in 1977 and, travelling at 11 miles per second, is now 137 AU from the Sun.

But the stars are far more distant than this. The nearest, Proxima Centauri, is about 270,000 AU, or 4.25 light years away. You would have to line up 30 million Suns to span the gap between the Sun and Proxima Centauri. The Vogons in Douglas Adams’s The Hitchhiker’s Guide to the Galaxy (1979) are shocked that humans have not travelled to the Proxima Centauri system to see the Earth’s demolition notice; the joke is just how impossibly large the distance is.

Four light years turns out to be about the average distance between stars in the Milky Way Galaxy, of which the Sun is a member. That is a lot of empty space! The Milky Way contains about 300 billion stars, in a vast structure roughly 100,000 light years in diameter. One of the truly exciting discoveries of the past two decades is that our Sun is far from unique in hosting a retinue of planets: evidence shows that the majority of Sun-like stars in the Milky Way have planets orbiting them, many with a size and distance from their parent star allowing them to host life as we know it.

Yet getting to these planets is another matter entirely: Voyager 1 would arrive at Proxima Centauri in 75,000 years if it were travelling in the right direction – which it isn’t. Science-fiction writers use a variety of tricks to span these interstellar distances: putting their passengers into states of suspended animation during the long voyages, or travelling close to the speed of light (to take advantage of the time dilation predicted in Albert Einstein’s theory of special relativity). Or they invoke warp drives, wormholes or other as-yet undiscovered phenomena.

When astronomers made the first definitive measurements of the scale of our Galaxy a century ago, they were overwhelmed by the size of the Universe they had mapped. Initially, there was great skepticism that the so-called ‘spiral nebulae’ seen in deep photographs of the sky were in fact ‘island universes’ – structures as large as the Milky Way, but at much larger distances still. While the vast majority of science-fiction stories stay within our Milky Way, much of the story of the past 100 years of astronomy has been the discovery of just how much larger than that the Universe is. Our nearest galactic neighbour is about 2 million light years away, while the light from the most distant galaxies our telescopes can see has been travelling to us for most of the age of the Universe, about 13 billion years.

We discovered in the 1920s that the Universe has been expanding since the Big Bang. But about 20 years ago, astronomers found that this expansion was speeding up, driven by a force whose physical nature we do not understand, but to which we give the stop-gap name of ‘dark energy’. Dark energy operates on length- and time-scales of the Universe as a whole: how could we capture such a concept in a piece of fiction?

The story doesn’t stop there. We can’t see galaxies from those parts of the Universe for which there hasn’t been enough time since the Big Bang for the light to reach us. What lies beyond the observable bounds of the Universe? Our simplest cosmological models suggest that the Universe is uniform in its properties on the largest scales, and extends forever. A variant idea says that the Big Bang that birthed our Universe is only one of a (possibly infinite) number of such explosions, and that the resulting ‘multiverse’ has an extent utterly beyond our comprehension.

The US astronomer Neil deGrasse Tyson once said: ‘The Universe is under no obligation to make sense to you.’ Similarly, the wonders of the Universe are under no obligation to make it easy for science-fiction writers to tell stories about them. The Universe is mostly empty space, and the distances between stars in galaxies, and between galaxies in the Universe, are incomprehensibly vast on human scales. Capturing the true scale of the Universe, while somehow tying it to human endeavours and emotions, is a daunting challenge for any science-fiction writer. Olaf Stapledon took up that challenge in his novel Star Maker (1937), in which the stars and nebulae, and cosmos as a whole, are conscious. While we are humbled by our tiny size relative to the cosmos, our brains can none the less comprehend, to some extent, just how large the Universe we inhabit is. This is hopeful, since, as the astrobiologist Caleb Scharf of Columbia University has said: ‘In a finite world, a cosmic perspective isn’t a luxury, it is a necessity.’ Conveying this to the public is the real challenge faced by astronomers and science-fiction writers alike.

We’re thrilled to announce that Welcome to the Universe, a guided tour of the cosmos by three of today’s leading astrophysicists, recently made the New York Timesextended bestseller list in science. Inspired by the enormously popular introductory astronomy course that Neil deGrasse Tyson, Michael A. Strauss, and J. Richard Gott taught together at Princeton, this book covers it all—from planets, stars, and galaxies to black holes, wormholes, and time travel. The authors introduce some of the hot topics in astrophysics in today’s Q&A:

What is the Cosmic Perspective?

NDT: A view bigger than your own that offers a humbling, yet enlightening, and occasionally empowering outlook on our place as humans in time, space, on Earth and in the Universe. We devote many pages of Welcome to the Universe to establishing our place in the cosmos – not only declarations of that place, but also the reasons and the foundations for how we have come to learn how we fit in that place. When armed with a cosmic perspective, many earthly problems seem small, yet you cultivate a new sense of belonging to the universe. You are, in fact, a participant in the great unfolding of cosmic events.

What are some of the takeaways from the book?

NDT: If you read the entire book, and if we have succeeded as authors, then you should walk away with a deep sense of the operations of nature, and an appreciation for the size and scale of the universe; how and why planets form; how and why we search for planets orbiting around other stars, and alien life that may thrive upon them; how and why stars are born, live out their lives and die; what galaxies are and why they are the largest organizations of stars in the universe; the large scale structure of galaxies and space-time; the origins and future of the universe, Einstein’s relativity, black holes, and gravitational waves; and time travel. If that’s not enough, you will also learn about some of the continued unsolved mysteries in our field, such as dark matter, dark energy, and multiverses.

This book has more equations than do most popular books about astrophysics. Was that a deliberate decision?

MAS: Yes. The book’s subtitle is “An Astrophysical Tour,” and one of our goals in writing it was to show how observations, the laws of physics, and some high school mathematics can combine to yield the amazing discoveries of modern astrophysics: A Big Bang that happened 13.8 billion years ago (we show you how that number is determined), the dominant role dark matter has in the properties of galaxies (we tell you how we came to that conclusion), even the fact that some planets orbiting other stars have conditions conducive for liquid water to exist on their surface, thought to be a necessary prerequisite for life. Our goal is not just to present the wonders of the universe to the reader, but to have the reader understand how we have determined what we know, and where the remaining uncertainties (and there are plenty of them!) lie.

So your emphasis is on astrophysics as a quantitative science, a branch of physics?

MAS: Yes. We introduce the necessary physics concepts as we go: we do not expect the reader to know this physics before they read the book. But astrophysicists are famous (perhaps notorious!) for rough calculations, “to astrophysical accuracy.” We also lead the reader through some examples of such rough calculations, where we aim to get an answer to “an order of magnitude.” That is, we’re delighted if we get an estimate that’s correct to within a factor of 2, or so. Such calculations are useful in everyday life, helping us discriminate the nonsensical from the factual in the numerical world in which we live.

Can you give an example?

MAS: Most people in everyday discourse don’t think much about the distinction between “million,” “billion,” “trillion,” and so on, hearing them all as “a really big number,” with not much difference between them. It is actually a real problem, and the difference between Federal budget items causing millions vs. billions of dollars is of course huge. Our politicians and the media are confusing these all the time. We hope that the readers of this book will come away with a renewed sense of how to think about numbers, big and small, and see whether the numbers they read about in the media make sense.

Is time travel possible?

JRG: In 1905 Einstein proved that time travel to the future is possible. Get on a rocket and travel out to the star Betelgeuse 500 light-years away and return at a speed of 99.995 % the speed of light and you will age only 10 years, but when you get back it will be the year 3016 on Earth. Even though we have not gone that fast or far, we still have time travelers among us today. Our greatest time traveler to date is the Russian cosmonaut Gennady Padalka, who by virtue of traveling at high speed in low Earth orbit for 879 days aged 1/44 of a second less than if he had stayed home. Thus, when he returned, he found Earth to be 1/44 of a second to the future of where he expected it to be. He has time traveled 1/44 of a second to the future. An astronaut traveling to the planet Mercury, living there for 30 years, and returning to Earth, would time travel into the future by 22 seconds. Einstein’s equations of general relativity, his theory of curved spacetime to explain gravity, have solutions that are sufficiently twisted to allow time travel to the past. Wormholes and moving cosmic strings are two examples. The time traveler can loop back to visit an event in his own past. Such a time machine cannot be used to journey back in time before it was created. Thus, if some supercivilization were to create one by twisting spacetime in the year 3000, they might use it to go from 3002 back to 3001, but they couldn’t use it go back to 2016, because that is before the time loop was created. To understand whether such time machines can be realized, we may need to understand how gravity works on microscopic scales, which will require us to develop a theory of quantum gravity. Places to look for naturally occurring time machines would be in the interiors of rotating black holes and at the very beginning of the universe, where spacetime is strongly curved.

Do we live in a multiverse?

JRG: A multiverse seems to be a natural consequence of the theory of inflation. Inflation explains beautifully the pattern of slightly hotter and colder spots we see in the Cosmic Microwave Background Radiation. It explains why the universe is so large and why it is as smooth as it is and still has enough variations in density to allow gravity to grow these into galaxies and clusters of galaxies by the present epoch. It also explains why the geometry of the universe at the present epoch is approximately Euclidean. Inflation is a period of hyperactive accelerated expansion occurring at the beginning of our universe. It is powered by a large vacuum energy density and negative pressure permeating empty space that is gravitationally repulsive. The universe doubles in size about every 3 10-38 seconds. With this rate of doubling, it very quickly grows to enormous size: 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024… That explains why the universe is so large. When the high density vacuum state decays, it doesn’t do so all at once. Like water boiling in a pot, it does not turn into steam all at once, but should form bubbles. Each expanding bubble makes a universe. The inflationary sea should expand forever, creating an infinite number of bubble universes, ours being one of them. Other distant bubble universes are so far away, and the space between us and them is expanding so fast, that light from them may never reach us. Nevertheless, multiple universes seem a nearly inevitable consequence of inflation.

What discovery about the universe surprises or inspires you the most?

JRG: Perhaps the most amazing thing about the universe is that it is comprehensible to intelligent, carbon-based life forms like ourselves. We have been able to discover how old the universe is (13.8 billion years) and figure out many of the laws by which it operates. The object of this book is to make the universe comprehensible to our readers.

Don’t miss this C-Span video on the book, in which the authors answer questions about the universe, including how it began and the likelihood of intelligent life elsewhere.

Neil deGrasse Tyson is director of the Hayden Planetarium at the American Museum of Natural History. He is the author of many books, including Space Chronicles: Facing the Ultimate Frontier, and the host of the Emmy Award–winning documentary Cosmos: A Spacetime Odyssey. Michael A. Strauss is professor of astrophysics at Princeton University. J. Richard Gott is professor of astrophysics at Princeton University. His books include The Cosmic Web: Mysterious Architecture of the Universe (Princeton).

We’re thrilled to launch this beautiful companion website to the highly anticipated new book, Welcome to the Universe by Neil DeGrasse Tyson, Michael Strauss, and Richard Gott.

If you’ve ever wondered about the universe and our place in it, then this elegant mini-tour of the cosmos is for you. Divided into three parts called ‘Stars, Planets and Life,’ ‘Galaxies,’ and ‘Einstein and the Universe,’ the site is designed to take you on a journey through the major ideas in Welcome to the Universe. We hope you learn something new and exciting about outer space. If you find something interesting and would like to share, please do! The site is set up to make sharing interesting tidbits on social media easy. Want to learn more? The site also includes information on where to learn more about each topic. Keep an eye out for the book in October 2016.

Today marks a new era in cosmology, astronomy, and astrophysics. The main page of the Einstein Papers Project website reports, “Gravitational waves do exist, as has been announced today with great joy by the scientists of the LIGO collaboration, after more than two decades of intensive experimental work.”

The cosmic breakthrough, which proves Einstein’s 100 year old prediction, has resulted in a tremendous response across the scientific community and social media. Scientific websites everywhere are already debating the meaning of the discovery, the #EinsteinWasRight hashtag has been bantered about on Twitter; You Tube featured a live announcement with over 80,000 people tuning in to watch (check it out at 27 minutes).

“The LIGO announcement today and the accompanying papers are totally persuasive. We all believed that Einstein had to be right in predicting gravitational waves, but to see them, so clean and so clear is marvelous. Two independent instruments saw the same signal from the same event, and it was just what had been predicted for the in-spiral and merger of two massive black holes.

A quarter of a century ago I had a bet with Kip Thorne that we would not see gravitational waves before the year 2000 – and I won that bet and a case of wine. But I did not doubt that, when the sensitivity of the instruments improved enough, gravitational waves would be found. Now the skill and perseverance of the experimentalists and the support of NSF has paid off.

“One hundred years ago in February 1916, Einstein mentioned gravitational waves for the first time in writing. Ironically it was to say that they did not exist. He said this in a letter to his colleague Karl Schwarzschild, who had just discovered the solution to Einstein’s equations which we now know describe black holes. Today brings a major confirmation of the existence both of gravitational waves and black holes. Yet Einstein was repeatedly skeptical about whether either of these ideas were really predictions of his theory. In the case of gravitational waves he soon changed his mind in 1916 and by 1918 had presented the first theory of these waves which still underpins our understanding of how the LIGO detectors work. But in 1936 he changed his mind again, submitting a paper to the Physical Review called “Do Gravitational Waves Exist?” in which he answered his own question in the negative. The editor of the journal responded by sending Einstein a critical referee’s report and Einstein angrily withdrew the paper and resubmitted it elsewhere. But by early the next year he had changed his mind again, completely revising the paper to present one of the first exact solutions for gravitational waves in his theory. So his relationship with gravitational waves was very far from the image of the cocksure, self-confident theorist which dominates so many stories about Einstein. Because of this, he would have been thrilled today, if he were still alive, to have this major confirmation of some of the most esoteric predictions of his theory.”

Here at Princeton University Press where we recently celebrated the 100th anniversary of Einstein’s theory of general relativity, the mood has been celebratory to say the least. If you’d like to read the Einstein Papers volumes that refer to his theory of gravitational waves, check out Document 32 in Volume 6, and Volume 7, which focuses on the theory. Or, kick off your own #EinsteinWasRight celebration by checking out some of our other relevant titles.

Astronomers study the oldest observable stars in the universe in much the same way that archaeologists study ancient artifacts on Earth. Stellar archaeologist Anna Frebel is credited with discovering several of the oldest and most primitive stars, and her book, Searching for the Oldest Stars is a gripping firsthand account of her work. Recently she took the time to answer some questions:

What is your main research topic and what is stellar archaeology?

AF: My work is broadly centered on finding the oldest stars in the universe and using them to explore how the first stars and the first galaxies formed soon after the Big Bang. This works because these ancient stars are about 13 billion years old and they are still shining. The universe itself, by comparison, is 13.8 billion years old. I find these ancient stars in the outskirts of the Milky Way galaxy, using a large telescope. I’m also researching how the chemical elements heavier than hydrogen and helium were first created in those early stars, which ultimately allowed Earth to form and to bring about life in the universe.

What is your biggest discovery?

AF: I have been fortunate enough to discover several “record holding stars”. In 2007, I found a 13.2 billion year-old star, which is incredibly old. This followed the 2005 discovery of the chemically most primitive star – a star of the second generation of stars to have formed in the universe. Since then, I have analyzed some incredible ancient stars in dwarf galaxies that orbit the Milky Way galaxy, and together with my team, we have recently beaten said 2005 record, which was enormously exciting.

Why do people say we are made from stardust?

AF: We humans are made from all sorts of different chemical elements, mostly carbon. We breathe oxygen and nitrogen, we wear silver and gold jewelry. All these elements were once, atom by atom, created inside different kinds of stars and their supernova explosions over the course of billions of years. Studying this evolution of the chemical elements in the universe with the help of ancient stars means that I’m literally studying the cosmic origins of the building blocks of life. So we really are closely connected with the universe, far more than we realize.

How did you decide to become a scientist?

AF: From a young age I knew I wanted to study stars. They were just so fascinating to me, these big spheres of gas, fusing new elements to gain energy to shine for eons in the sky. Fortunately, I received good advice during high school on how to become an astronomer. After studying physics until 2002, I turned to astronomy and the rest is history. Today, I take pride in sharing my story with young people and the general public by telling them what astronomers do on a daily basis, and how scientific results are achieved. I am passionate about conveying the importance of science literacy to the young and the young at heart while inspiring them with the beauty and mystery of the cosmos.

What kind of telescope is used for your astronomical observations?

AF: Astronomers use all kinds of different telescopes on Earth as well as from space to peer deep into the cosmos. It depends on the type of project and the brightness of the objects which telescope is best suited. Space observations are being carried out remotely, whereas ground-based observations are still done by the astronomer who has to travel to the telescope. More and more telescopes are becoming automated to enable remote controlled “office observing”.

Anna Frebel in front of the 6.5m Magellan Telescope in Chile.

Are you traveling to any telescopes?

AF: Yes, I regularly fly to Chile to the Magellan Telescopes to carry out my observations. These are some of the largest telescopes in the world and the dark night sky in the Southern Hemisphere is terrific for studying the cosmos. It’s the favorite part of my job and I love discovering new facts about the universe through these observations!

What does it mean when you say you’re going observing?

AF: To use the telescopes, you have to fly to Chile. First to Santiago, then to La Serena and from there is a 2-3h drive up the mountains of the Atacama Desert where the telescopes are. There are guest rooms there for the observers to sleep during the day and the observatory chefs are cooking delicious meals for everyone. Dinner is eaten together by all observers, including the technical staff. It’s a little community with the sole purposes of caring for the telescopes and obtaining exquisite astronomical observations all night long of a breathtaking sky.

What does a typical night at the telescope look like?

AF: All preparations for the night happen during the afternoon while it’s still light outside. After sunset, I usually choose the first targets from my list, which I begin to observe soon after dark. Each star is observed for 10-30 minutes. We immediately inspect each observation and then decide on the fly whether we need more data or not. If we have found an interesting old star we may choose to immediately observe it for a few more hours.

Did anything ever go wrong at the telescopes?

AF: Of course! Mostly when it’s cloudy because then we can’t observe any starlight. This can be very frustrating because it can mean that we have to come back to the telescope a year later to try again. Clouds spell bad luck. Other times, the air layers above the telescope are often not as smooth as is required. This makes the stars twinkle and appear less sharp, which means less good data and longer exposure times. And sometimes there are technical problems with the telescope too.

How do you get your telescope time? Can I go to your telescope and observe, too?

AF: To obtain telescope time, astronomers have to submit a proposal to a committee that selects the best projects and awards them the time. The proposal contains a detailed description of the project and the technical details on what information is being sought. Telescope use is restricted to professional astronomers because of the considerable expense. The cost is about USD 50,000 to 100,000 per night, depending on the telescope, and often paid by various institutions and universities who jointly operate observatories. While this is a lot of money, it’s actually not that much in comparison to many other research facilities.

Are there any special moments at the telescope that you remember in particular?

AF: Yes, going observing is always magical and memorable. Of course I particularly remember big discoveries and the excited nervousness of checking and checking whether we didn’t make a mistake and that the discovery was really what it appeared to be. Then, there have been the frustrating moments of sitting at the telescopes for nights on end listening to the rain and flying home empty-handed. I have been there when severe technical problems and even a bush fire prevented observing during clear nights. But I always associate observing with the most colorful sunsets, the calm and peaceful atmosphere up in the mountains, and of course the sleepless but exciting nights.

Anna Frebel is the Silverman (1968) Family Career Development Assistant Professor in the Department of Physics at the Massachusetts Institute of Technology. She is author of Searching for the Oldest Stars, and has received numerous international honors and awards for her discoveries and analyses of the oldest stars. She lives in Cambridge, Massachusetts.

Business Insider included Katherine Freese, author of The Cosmic Cocktail, in a list of the 50 scientists who are changing the world. Freese was recognized for her pioneering work in the study of dark matter. Other picks included Andrea Accomazo, the first person to land a probe on a comet, Alan Stern, the principal investigator for NASA’s New Horizons mission, Cori Bargmann, autism and Alzheimer’s researcher, as well as an impressive lineup of other scientists whose “revolutionary research in human happiness, evolutionary biology, neutrino physics, biotechnology, archeology, and other fields is helping to advance our lives in more ways than we could ever imagine.”

You can read the full feature here, and watch Freese discuss the greatest mysteries of the universe here.

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